Mail.app not starting after Lion upgrade

maybe i am not getting this, but I cannot find mail in my library. I type library in the search field and when i click on the folder the only file in there is a font folder...... what am i doing wrong????

Tim Your awesome!! I have been fighting with my email all day and I did exactly what you said and it worked. Thank you Thank you!!

I've had the same problem following my upgrade from Snow Leopard to Lion. I tried the advice about trashing the Envelope Index files, but that only allows the updater to go through the "Importing Mailboxes" stage. It still crashes at the "Migrating Data" stage. Any suggestions?

Removing the index files worked for me, too. Thanks all.